I’ve been wearing a pre-introduction unit of a Phosphor watch made by an 18-month old company called Art Technology of Hong Kong. The watch has a striking design, but the reason you’re reading about it here is that it has an electrophoretic display (EPD), which is unusual for watches. Indeed, the only other one I know of is a previous, somewhat more conventional looking, model introduced by Art Tech last year. EPDs are, of course, better known for being the display of choice in eBook readers such as Amazon’s Kindle.

Ken Werner
Senior Analyst and Editor

The watch I’m wearing — called the "Digital Hour Clock", which is one of two models formally introduced the day before yesterday — has a curved stainless steel case that is more or less rectangular when viewed from the front but is not particularly thin at 8.0mm. The case has a satin finish on the front, but is polished to a mirror finish on the edges and back.

The display covers most of the front of the watchcase, but not quite as much as the photo suggests. There is a glossy black border between the display and the stainless steel bezel, and the display’s dark background is not as black as the border, although it still provides a high-contrast display. What is striking is that the curved display, made by E Ink, exactly matches the curvature of the case. The display itself is only 400 micrometers thick. Although it’s a segmented display, the segments are designed so they flow into each other, and the forms of the digits are smooth and distinctive.

Several display modes can be selected: graphic (shown) and all-digital presentations of time, month/day, and alarm. The press of a button reverses the polarity of the display, and the display automatically reverses polarity each minute when the display changes. There is no indicator for seconds on this watch.

So why select an EPD for a watch display? In fact, why commit yourself to using nothing but EPDs in your entire watch line, which is what Art Tech has done.

For answers, we exchanged e-mails with Donald Brewer, co-founder of Art Tech and head of Bandit, Inc., Art Tech’s U.S. distributor. It’s worth saying that Brewer knows something about watches, since he was previously VP of Technology at Fossil.

"I believe there is an upscale market and interest in a more fashionable digital watch," said Brewer, "but that requires a display technology like E Ink that has several unique features/capabilities to differentiate it from the LCDs typically used." Among these features are much greater brightness than LCDs, higher contrast, and the ability to have a curved display.

Here are the questions and answers that followed:

Display Daily: The watch design makes use of the display’s flexibility for its nicely curved shape and surface, but it does not exploit the display’s thinness; the case is quite thick. Why is that?

Donald Brewer: Although the E Ink display is noticeably thinner than a glass LCD, our target customer on these first versions are the type of customer purchasing the thicker, more bulky, stylish digitals you might find from brands such as DIESEL. We also exploit a few additional advantage of E INK with the invertible / changeable display, and of course the much higher contrast ratio. I expect that our next generation designs may go after a thin, and possibly even flexible watch design.

DD: The display has no second indicator. That should increase battery life since the display only needs to be updated once a minute. So battery life should be long. I was therefore surprised to see you have used a rather large battery, a CR2025. Why is that? How long do you project battery life will be?

DB: E Ink’s bi-stability is an advantage in a watch application. A secondary issue is that typically a watch has a 3V battery, but E Ink displays require a higher voltage. The additional power consumption of the higher voltage offsets some of the advantages of zero power consumption between transitions, but we still get around 18-24 months battery life with a standard watch-sized battery.

DD: You’ve put an MSRP of $175 to $200 on the watch. What do you see as your market niche? Who is your target buyer?

DB: We are targeting the high-end digital market. I think that customers do have an affinity for digital watches, but due to commoditized LCDs, digital watches have come to be associated with the $2.99-$19.99 digital watches you might find in a drugstore. I think that E Ink displays offer a number of differentiating features from the standard black-on-grey LCDs that can be used to create a line of digital watches with higher perceived value.

Well, that’s the view of the product guy. We then directed some questions to the display guy, E Ink’s Marketing VP Sri Peruvemba.

DD: When the display in the Phosphor watch updates on the minute, it also inverts the display polarity. Is that a design choice from Art Technology, or is there a technical reason for doing that?

SP: It’s a design choice from the customer.

DD: When the display inverts, it also flashes to full-screen black and full-screen white first. Is this done to clear the display of ghost images?

SP: It is indeed to prevent ghosting. But it does not have to be at every refresh. This reflects design guidelines from earlier versions that have carried through. Typically, the designer makes the choice of refresh frequency

DD: What voltage is used to drive the display in the Phosphor watch? What kind of power supply is used to increase the voltage from the battery’s 3V?

SP: Fifteen volts, as in all of our displays. There are charge pumps in the display controller that boost the voltage up. The power saving is significant in larger displays but in a small display that refreshes constantly, you are not taking full advantage of the bistable nature of the EPD technology.